78 MICRO-ORGANISMS AND FERMENTATION. 



be either straight or somewhat curved. The rods are seen 

 in brisk movement, and under a strong magnifying power they 

 are found to be covered with a large number of cilia. Before 

 the formation of spores in the rods, the latter swell and 

 form peculiar spindle and lemon-shaped, elliptical, or club- 

 like forms (see fig.) ; at the same time it is remarkable to 

 note that they are coloured blue by iodine. On germination 

 the spores burst their outer envelope, and the germ filament 

 grows in the same direction as the longitudinal axis of the 

 spore. Clostridium lutyricum grows most readily at a tempera- 

 ture of about 40 C., and rapidly predominates in a sugar solution 

 if the lactic acid ferment has previously converted a portion of 

 the sugar into lactic acid. This species is decidedly anaerobic. 



FITZ has described a species belonging to the aerobic 

 organisms. It is a bacillus of a short cylindrical form, which 

 is not coloured blue by iodine, is motile in a moderate degree, 

 and forms no spores. It ferments all carbohydrates, with the 

 exception of starch and cellulose. 



HUEPPE has likewise described a species found in milk, and 

 occurring in the same forms as the species discovered by 

 PRAZMOWSKI, but it proved much less sensitive towards 

 oxygen, and must therefore be classed with the aerobic species. 



GRUBER found associated under the name of Clostridium 

 butyricum three well-defined species, two of which are 

 exclusively anaerobic. One of the latter species consists of 

 straight or slightly-curved rods, which become spindle- or 



from the test-tube by means of an air pump, the tube being kept in water at 

 30-35 C. ; it is then closed or hermetically sealed. Another way is to pass 

 a current of hydrogen through the nutritive liquid containing the growth 

 in the test-tube, which is closed hermetically as soon as the atmospherical 

 air has been expelled ; then the glass is rotated on its longitudinal axis 

 until the gelatine has coagulated and the inside of the glass is coated by 

 it ; in this gelatine coating the colonies gradually make their appearance. 

 Substances that absorb oxygen may also be used, such as pyrogallic acid 

 (1 gram of this acid in 10 c.c. of 10 per cent, caustic potash solution), the open 

 test-tube or the plate-culture being placed in an air-tight tube or vessel 

 containing the reagent ; or, again, the cultures may be covered with paraffin, 

 vaseline, oil, plates of mica, or the like. An addition of grape-sugar and 

 slight quantities of sodium formate or the sodium salt of indigo mono- 

 sulphonic acid to the nutritive substance renders the medium particularly 

 favourable for these bacteria. 



